In areas in which earthquakes frequently occur, it is desirable that any line supplying natural gas to a building contain an automatic shut off valve for closing the gas supply line in response to earthquake forces, in order to minimize the possibility of a disastrous fire. Various types of actuators have been devised for this purpose, typically including an inertia actuated weight displaceable by shock forces in a manner operating or releasing a mechanism for closing the valve or attaining another desired safety purpose. One such device is shown in U.S. Pat. No. 4,185,507 issued Jan. 29, 1980 to Frank F. Domyan for "Acceleration Responsive Tripping Mechanism". In that device, a weight is supported on an upper surface of a pedestal, with a surrounding tube yieldingly urged upwardly and being actuable downwardly by the weight when the weight is displaced laterally by shock forces.